How to rotate a union with Tween Service?

I tried 2 ways to rotate it, but none worked. Here are my scripts: 1st method:

spawn(function()
    while true do
        local tween = tweenService:Create(child, TweenInfo.new(1), {Orientation = union.Orientation + Vector3.new(120, 0, 0)})
        tween:Play()
        tween.Completed:Wait()
    end
end)

2nd method:

spawn(function()
    while true do
        local tween = tweenService:Create(union, TweenInfo.new(1), {CFrame = union.CFrame*CFrame.Angles(120, 0, 0)
        tween:Play()
        tween.Completed:Wait()
        local tween2 = tweenService:Create(union, TweenInfo.new(1), {CFrame = union.CFrame*CFrame.Angles(240, 0, 0)
        tween2:Play()
        tween2.Completed:Wait()
        local tween3 = tweenService:Create(union, TweenInfo.new(1), {CFrame = union.CFrame*CFrame.Angles(360, 0, 0)
        tween3:Play()
        tween3.Completed:Wait()
    end
end)