Shielded Metal Arc Welding Design for Construction Joint

Shielded Metal Arc Welding Design for Construction Joint - Construction in the machine design is a static part of the most important in building a machine that is strong, stable and aesthetics. Machine construction isn’t only formed by a solid component, but strung together by two or more components that are becoming an integral component assembly machine. Machine construction powerful should be supported by a strong joint between components as well. Many types of construction joint are used in the assembly process of the machine construction such welding joint, folding joint, rivet joint, bolt joint etc.

In this article only focuses on welding joint used in the assembly process. Welding joint is one type of the fixed joint that is a connection that can’t be released again except by destroying it. Many types of welding but in this post I will explain the arc welding process, more specifically about how to design a construction joint by shielded metal arc welding.

Prior to the main topic, we must first know what it is the shielded metal arc welding. Shielded metal arc welding (SMAW) is a manual arc welding process in which welding heat generated by the electric arc formed between the electrodes shielded flux with the workpiece. Shielded metal arc welding has been chosen by the designer in the design process of construction machinery as it has many advantages such as (1) the initial investment cost is low, (2) a reliable and simple operation, (3) the filler material (electrode) cost is low, (4) filler material can vary, (5) can use the same equipment for all types of material, (6) can be done to part with a variety of thicknesses and (7) can be done for all position welding.

When you will design the machine construction with welded joints strong, to note that the value must be greater welding strength of the welding stress occurs, otherwise it will lead to plastic deformation, cracks or broken. Welding strength is affected by the electrode material and the material properties of the main metal while welding stress is affected by the welding dimension and load.

Welding Electrode for Shielded Metal Arc Welding 

Electrode used for shielded metal arc welding is a type of metal electrode wire wrapped in flux. Electrode metal removal process occurs when the tip of the electrode melts and forms the items carried by the arc electric current.

Selection of electrode is determined by the type of wire and flux are used with reference to the code electrode according to the classification AWS (American Welding Society). According to the classification AWS (American Welding Society), the electrode of mild steel and low alloy steel for electric arc welding expressed by the code:

Note:
1. E    = Electrode of arc welding
2. XX = Tensile strength (thousands Psi)
3. X    = Welding position
4. X    = Type of flux and current suitable for welding

Example:

E 6013, which means arc welding electrodes with a minimum tensile strength of 60,000 psi or 42.2 kg / mm2, can be used for all position welding, flux type is the high potassium titanium and electric current with AC or DC+ or DC.

The table below is a list of electrode classification code of mild steel according to AWS A.5.1-64T.

Code	Type Flux	Welding Position	Electric Current
E60 Group = Minimum tensile strength after welded is 60.000 Psi or 42,2 kg/mm2
E6010	High Cellulose Sodium	F, V, OH, H	DCR
E6011	High Cellulose Potassium	F, V, OH, H	DCR - AC
E6012	High Titanium Sodium	F, V, OH, H	DCS - AC
E6013	High Titanium Potassium	F, V, OH, H	DCR - DCS - AC
E6020	High Iron Oxide	F, H	DCR - DCS - AC
E6027	Iron Powder, Iron Oxide	F, H	DCR - DCS - AC
E70 Group = Minimum tensile strength after welded is 70.000 Psi or 49,2 kg/mm2
E7014	Iron Powder, Titanium	F, V, OH, H	DCR - DCS - AC
E7015	Low Hydrogen Sodium	F, V, OH, H	DCR
E7016	Low Hydrogen Potassium	F, V, OH, H	DCR - AC
E7018	Iron Powder, Low Hydrogen	F, V, OH, H	DCR - AC
E7024	Iron Powder, Titanium	F, H	DCR - DCS - AC
E7028	Iron Powder, Low Hydrogen	F, H	DCR - AC
Note:      Welding Position                 F = Flat                 V = Vertical                 OH = Overhead                 H = Horizontal		Note :     Electric Current                 DC = Direct Current                 AC = Alternating Current                 DCR = DC Reverse Polarity                 DCS = DC Straight Polarity

Based on the table above, the minimum tensile strength after welding related to the weld traction properties associated with tensile testing. In the weld joint, capable of tensile properties strongly influenced by the primary metal properties, HAZ regions, weld metal (electrode core wire) and the dynamic properties of the welding joint.

Welding Stress

What is meant by welding stress herein include tensile stress, bending stress and welding efficiency. How welding strength designed for a connection in machine construction design, the following I will explain one by one according to welding stress that occurs in the welding joint.

(1) Tensile Stress 

Welding joint will experience tensile stresses if there is tensile load or force acting on the cross section of the weld results. Tensile stress of welding joint is affected by welding load and cross-sectional area with the following formula.

Note:
s_t = Tensile Stress (kg/mm2)
F = Force or Welding Load (kg)
A = Cross-sectional area (mm2)

Force or welding load in construction joint can be caused by cutting force, part weight that is supported by construction, tightening force of bolt etc.

Cross-sectional area of the welding joint has a different value depending on thickness and length of the weld seam. Weld seam has a different shape according to the type of welding joint as blunt joint, T-joint, cross joint, edge joint, joint angle and overlap joint (read more in the Type of Welding). Type of seam welding is i-seam, v-seam, v-tapered seam, u-seam, double V-seam, k-seam etc.
Therefore, the tensile stress in welding joint for each type of seam welding would have a different formula. (Formulas related to the tensile stress on each type of seam welding you can see on the post Seam Welding Design).

(2) Bending Stress

Welding Joint will experience a bending stress if there is bending load acting on the cross section of the weld results. Bending loads occur due to the force that causes the bending moment on the cross section of the weld results. As well as tensile stress, bending stress formula also depends on the type of welding joint and seam welding. But in general the bending stress that occurs in the welding joint can be formulated as follows:

Note:

s_b = Bending Stress (kg/mm2)

M   = Bending Moment (kgmm)

h = Seam Thickness (mm)

l = Seam Length (mm)

(3) Welding efficiency

Welding efficiency is defined as a decrease factor of the allowable stress of main metal which is formulated as follows:

Note:

h   = Welding efficiency

σ_w  = Allowable Stress of Welding Joint (kg/mm2)

σ    = Allowable Stress of Main Metal (kg/mm2)

The value of the welding efficiency is determined by the welding material, welding method, inspection method and conditions of use connection.

That is a description about Shielded Metal Arc Welding Design for Construction Joint. If you find misconceptions in the arc welding formula, please provide the correction in the comment box.

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Ball Bearing Selection Guide: Sizes, Life Time and Lubrication

Ball Bearing Selection Guide: Sizes, Life Time and Lubrication - Bearing is standard parts that we often encounter in most of the moving tool both manual tools and electrical tools. What is bearing? Bearing is the machine parts that supporting the rotating shaft or moving straight shaft. Bearing able to keep a straight shaft rotation or movement can take place in a smooth, safe and long lifespan. Bearings should be sturdy enough to allow the shaft as well as other machine parts work well. If the bearing isn’t functioning properly, then the achievements of the entire system will decrease or can’t work properly.

Many types of bearings used in industrial machinery including ball bearing, roller bearings, thrust bearings, needle bearings, spherical bearings, tapered bearings etc. Each type of bearing has advantages and disadvantages in accordance with their respective functions. In this post I will explain about the ball bearing mainly on the topic of how to choose a ball bearing based on sizes, life time and lubrication.

Before getting into the topic of ball bearing selection guide, we must be known what it is ball bearing? Ball Bearings are a type of rolling-element bearing that uses balls to maintain the separation between the moving parts of the bearing. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. Ball bearing construction consists of outer ring, inner ring, steel ball, cage and shield as in the image below.

An advantages of ball bearing is at a very low friction. Lubrication was also very simple, just with grease, even on ball bearings with shield no longer need lubrication. But in general, ball bearings are more suitable for small loads. Bearing speed is also limited by centrifugal force that occurs in the steel ball.

How to choose a good ball bearing based on sizes, life time and lubrication, the following explanation:

Selection of the ball bearing sizes

Ball bearing sizes selected from a catalog of standard bearings. Although different brands of bearings, but usually bearing the same code as standard. The ball bearing code refers to the size of the inner ring diameter, outer ring diameter, and width. In general, the inner ring diameter is taken as a benchmark, then the outer ring diameter and width adjust to various alternative sizes.

The ball bearing code consists of basic and supplementary numbers as below:

Note:

• Type, bearing types, as 6 = Deep Groove Ball Bearing
• Series, outer ring diameter, as 0 = Extra Light, 2 = Light, 3 = Medium, 4 = Heavy etc. (see Table of Code Deep Groove Ball Bearings)
• Bore, inner ring diameter, as 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm and 04 to 96 is bore sizes x 5 mm, for example if bore is 05 so the inner ring diameter is 05 x 5 mm = 25 mm.
• Sealing, bearing seal or shield, as RSR = Standard Rubber Seal, HSR = Hycar Seal, VSR = Viton Seal, ZR = Metal Shield, 2ZR = 2 Metal Shield etc.
• Radial Clearance, radial clearance class, as CN = Normal Clearance, C1 = Clearance Class 1 etc
• Precision Class, as PN = Normal Precision Class, P1= Precision Class 1 etc.

Table of ball bearing sizes for type of the deep groove ball bearing is below:

Deep Groove Ball Bearing Sizes
Code	Dimensions (mm)				Code	Dimensions (mm)				Code	Dimensions (mm)
	d	D	B			d	D	B			d	D	B
6000	10	26	8		6200	10	30	9		6300	10	35	11
6001	12	28	8		6201	12	32	10		6301	12	37	12
6002	15	32	9		6202	15	35	11		6302	15	42	13
6003	17	35	10		6203	17	40	12		6303	17	47	14
6004	20	42	12		6204	20	47	14		6304	20	52	15
6005	25	47	12		6205	25	52	15		6305	25	62	17
6006	30	55	13		6206	30	62	16		6306	30	72	19
6007	35	62	14		6207	35	72	17		6307	35	80	21
6008	40	68	15		6208	40	80	18		6308	40	90	23
6009	45	75	16		6209	45	85	19		6309	45	100	25
6010	50	80	16		6210	50	90	20		6310	50	110	27
6011	55	90	18		6211	55	100	21		6311	55	120	29
6012	60	95	18		6212	60	110	22		6312	60	130	31
6013	65	100	18		6213	65	120	23		6313	65	140	33
6014	70	110	20		6214	70	125	24		6314	70	150	35
6015	75	115	20		6215	75	130	25		6315	75	160	37
6016	80	125	22		6216	80	140	26		6316	80	170	39
6017	85	130	22		6217	85	150	28		6317	85	180	41
6018	90	140	24		6218	90	160	30		6318	90	190	43
6019	95	145	24		6219	95	170	32		6319	95	200	45
6020	100	150	24		6220	100	180	34		6320	100	215	47
Note : d = Inner Ring Diameter, D = Outer Ring Diameter, B = Bearing Width

Determine of the ball bearing life time

Ball bearing life time is the ability to hold the load bearing acting on it both radial force and axial force. The greater ability to withstand load bearing, it will be the longer life of the bearing. Therefore, when we choose a ball bearing sizes, we have to consider the bearing life through:

(1) Determine the equivalent load on bearing

Equivalent load is a load that causes deformation when there is contact between the steel balls with a ring at the maximum stress. Equivalent load can be calculated using the formula:

Note:

P = Equivalent load (kg)

X = Radial force factor

F_r = Radial force (kg)

Y = Axial force factor

F_a = Axial Force (kg)

(2) Determine the bearing capacity

Bearing capacity is the limit strength or ability of ball bearing in the receiving load. Based on data from the ball bearing code for the selected of ball bearing sizes, bearing capacity can be determined by the following formula:

Note:

C = Bearing capacity (kg)

i = Total row per bearing

a = Contact angle (o)

Z = Total steel ball per row

D_a = Steel ball diameter (mm)

f_c = Bearing factor based on type, precision class and material

After knowing the equivalent load and bearing capacity, we can determine the bearing life time, as the ball bearing strength parameters. Ball bearing life time can be calculated using the formula:

Note:

L_h = Bearing life time (hour)

f_h   = Bearing life factor

where the bearing life factor can be calculated by the formula:

Note:

f_h  = Bearing life factor

fn = Bearing speed factor 

C = Bearing capacity (kg)

P = Equivalent load (kg)

where bearing speed factor is calculated by the formula:

Note:

fn = Bearing speed factor 

n = Bearing speed (rpm)

Lubrication of ball bearing

Once we choose a ball bearing size by considering the ball bearing life time, the next step is to perform maintenance on bearings so that the bearing life time is maintained. One form of treatment is to lubricate the bearings.

Lubrication of ball bearing aimed to (1) reduce friction and wear between the steel ball and cage, (2) carry out the heat that occurs, (3) to prevent corrosion and (4) avoid the entry of dust. There are two ways lubrication with grease lubrication and oil lubrication.

Grease lubrication is preferred because the sealing is simpler and all the grease of good quality can provide longevity. Common way of greasing is to fill the inside of the bearings with grease as possible.

Lubrication oil is a useful way of high speed or high temperature of bearing. The most popular is the bags lubrication. In the process of this lubrication, the oil must be loaded until the middle of the steel ball lowest. Oil temperature must be maintained through the cooling pipes or water circulation.

Ball bearing calculation formulas above is taken from the handbook of Design of Machine Elements by Sularso & Kiyokatsu Suga and Mechanical Engineering Design by Shigley & Mitchel

That is a description about Ball Bearing Selection Guide: Sizes, Life Time and Lubrication. If you find misconceptions in the ball bearing formula, please provide the correction in the comment box.

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