Shandon-Elliot Micro Spot Welder

The Shandon-Elliott Micro Spot Welder is a robust precision ma­chine, specially designed for the speedy and efficient welding of stainless steel, resistance and other ferrous wires and tapes. It incorporates variable power and timing controls and will weld wires, tapes, etc. ranging from .001 in. to .040 in. diameter or thickness, producing a perfect, homogeneous weld without destroying the temper of the material.

The machine is foot-controlled by means of a pedal, enabling the operator to use both hands for locating the work between the electrodes. Its built-in carrying handle and weight of only 35 Ib make it comple­tely portable. The machine is well finished in enamel with a stainless-steel top cover, handle supports and pilot lamp housing. The machine incorporates four top and four bottom ele­ctrode, mounted so that they be used in various combi­nations to weld similar or dif­fering sizes of tapes and wi­res. These eight interchangeable electrodes, made of a special alloy, fit into tapered sockets in rotatable stainless- steel chucks. They are num­bered for use with a combina­tion table on the right-hand side of the machine which in­dicates the correct power and time settings and the electrode combinations to be used for various classes of work. The electrodes are arranged as follows:

Top Electrodes: No 1—curved electrode with flat work­ing surface 1 mm in diame­ter.

No 2—straight electrode with two grooves at right angles to each other. The grooves are about 0.5 mm deep to accommodate 1 mm wire.

Nos 3 and 4—curved electrodes filed to chisel point, then edges filed flat to 0.5 mm wide Xl mm long. This permits welding in corners.

Bottom Electrodes: No 1—curved electrode with working surface slightly domed. This "marries" with Top No 1 electrode for tape weld­ings.

Nos 2,3 and 4—straight electrodes, all grooved to accommodate intermediate size wires from 0.35 mm to 1 mm. These "marry" with Top No 2 electrode for wire weldings.

The electrodes can easily be modified by the user or spare electro­des can be filed to shape to suit special requirements.

In operation, the appropriate electrodes and time and power set­tings are selected in accordance with the combination table fitted to the machine. The work is positioned between the electrodes, which are then brought together by initial pressure on the foot pedal, grip­ ping the work firmly. Further pressure on the foot pedal closes the cir­cuit and completes the weld.

TEXT 20

Metals and non-metals

The 105 elements do not, fortunately, exhibit 105 completely dif­ferent sets of properties. When the major properties are considered it is found that the elements fall into one of two groups, the metals or the non-metals. The contrast between the properties of these two groups is given below. It is not to be expected that all elements in one class will agree in every detail; some differ in one or two properties from the others of their class; these exceptions are indicated in brackets.

Metals Non-Metals

Physical properties

1. Solid at room. temperature (mercury is the only liquid metal) 2. Have a high density (except potassium and sodium) 3. Can be moulded by pressure, i. e. they are malleable 4. Have high melting points and boiling points 5. Are good conductors of heat and electricity 6. Can be drawn into wire, i.e. they are ductile

1. Many are liquids and gases at room temperature 2. Density is usually low 3. Solid non-metals are brittle 4. Have low melting points and boiling points 5. Are poor conductors of heat and electricity (graphite is a good conductor of electrici­ty) 6. Cannot be drawn into wire

Chemical properties

7. Have basic oxides 8. React with dilute acids form­ing salts 9. Form positive ions 10. Are liberated at the cathode during electrolysis (hydrogen acts as a metal)

7. Have acidic oxides 8. Salts of non-metals do not exist 9. Form negative ions 10. Are liberated at the anode during electrolysis

The chemical properties are much more conclusive than the phys­ical properties for deciding whether a particular element is to be re­garded as a metal or a non-metal, e.g.: if an element forms a basic oxi­de, it must be classified as a metal. A basic oxide is never formed by a non-metal. To determine if a particular element is a metal or a non-metal, pre­pare its oxide and examine this as follows:

a) if the oxide is soluble in water, use litmus to find out if the so­lution is acidic or alkaline;

b) if the oxide does not dissolve in water, an attempt must be made to find out if it neutralizes an acid and forms a crystalline salt. Only metallic oxides do this.

TEXT 21