1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156 
2. Welding Equipment
Page 73
If you've noticed an error in this article please click here to report it so we can fix it.
BY A. J. P. WILDING, A.M.I.MECH.E., 11/1.1.R.T.E.
A.R.O. MACHINERY CO. LTD.
190 Casteluau, London, S.W.13.
OF particular interest to operators in the equipment manufactured by this concern is the A.R.O. Special Repair Set which has been sold for a number of years for spot-welding repairs on commercial vehicles. The set consists of two types of gun and a control panel, carried in a specially designed trolley which keeps the items tidily together.
The two guns are the 169A pincer spot gun and the DP 38 twin-spot gun, The 169A is light, so that it can be operated easily with one hand—one handle controlling pressure and current. It is fully automatic with a built-in transformer and there are no trailing cables. The DP 38 twin-spot gun is for one-sided approach work, the current travelling from one prod through the work to the other. Two spot welds are normally made, but if only one spot is to be made a swivel-type electrode tip is available. With the model DP 38 it is possible to weld in the middle of large sheets as well as panels onto closed side-members, tophat sections, square or rectangular tubes, and so on. A version of this gun is the DP 39, 'which has the same characteristics but is fully water-cooled to allow higher production rates.
On mild-steel, the 169A gun has a capacity of two 14-s.w.g. sheets and weighs 23 lb. The DP 38 and 39 have a capacity to weld two 20-s.w.g. mild-steel sheets, but under the best conditions—where there is no line voltage drop and the sheets are very clean-the capacity can be increased to 18 s.w.g. onto 16 s.w.g. Various electrodes are available for the 169A, and a set of electrodeholders are available which extend the working reach to 1 ft. 6 in.
Both guns can be operated with A.R.O. D12 or CD12 automatic timer/contractor control units and the latter is supplied with the repair set. These units switch on the welding current immediately the pre-set weld pressure is reached and have a safety control system which cuts the electric supply to
the gun if an earth wire is faulty. Another feature is a thermic energy control which is adjustable to three positions and automatically adjusts the weld-current for irregularities of service conditions of the metal— such as dirt, scale or rust. A further advantage of the CD12 is that it has a weld current control adjustment which is for use when welding mild-steel sheet of 22 s.w.g. or lighter, and for all wire work.
Recent modification to the repair set is that the CD12 control panel is now fitted with printed circuits and an easy-to-replace relay system_ The transformer on the 169A gun is more compact in size than earlier models, but still produces between 8,000 and 9,000 amp, at not less than 2,2 V. In the case of the DP 38 and 39, 11,000 amp. are produced at an open-circuit voltage of 3.6 V.